1. Field of the Invention
This invention relates generally to the downloading of data to a digital telephone device. More particularly, it relates to the transmission of data to a digital telephone device over an analog communication link such as a telephone line using dual tone multiple frequencies (DTMF).
2. Background of Related Art
Digital telephone devices having processors and memory storage have become commonplace. For instance, digital voice messaging systems have become an everyday requirement in today's society. Early voice messaging systems comprised mechanical systems and magnetic cassette tapes. However, cassette tapes were disadvantageous because of the mechanics and time required. More recently, particularly as the size of memory has increased in density while at the same time decreased in price, digital voice messaging systems have gained in popularity. Digital voice messaging systems store incoming voice messages in digital memory, reducing the mechanics and cost, and increasing the reliability over conventional analog voice messaging systems.
Most digital telephone devices include a processor, memory and the capability to generate and detect dual tone multi frequency (DTMF) tones (also known as `touch-tone`) on a telephone line. DTMF tones were originally used by the telephone system to communicate keys pressed when dialing. Using this conventional method, each key on the telephone's 4.times.4 (or 3.times.4) keypad generates two simultaneous tones, one for the row and one for the column. The two simultaneous tones are decoded to determine which key was pressed.
FIG. 5 depicts the conventional 4.times.4 keypad including 16 keys. A 3.times.4 keypad is one which does not include keys 313-316.
Each of the 16 keys 301-316 corresponds to a unique combination of row and column DTMF frequencies. For instance, if any of the keys in the first row containing keys 301, 302, 303, 313 are pressed, then a tone from the low frequency group, i.e., 697 Hz, is output. A second tone from the high frequency group corresponding to the row of the key is also output simultaneously with the first tone. Thus, if key 301 is pressed, the dual tones 697 Hz and 1209 Hz are output simultaneously. Similarly, if key 302 is pressed, the dual tones 697 Hz and 1336 Hz are output, etc.
FIG. 6 shows a conventional digital telephone device 10, i.e., a telephone answering device (TAD) 10. The TAD 10 includes a telephone line interface (TLI) 48, which interfaces to a telephone line 14 from a central office 13. A processor (such as a microprocessor, microcontroller, and/or digital signal processor (DSP) 18 controls the operation of the TAD 10. The processor 18 receives input from a local 4.times.4 or 3.times.4 keypad 36, and displays information relating to the operation of the device on a display 27. The processor 18 also controls the recording and playback of voice messages through a voice recorder/playback module 20, including a microphone 106 and speaker 108.
The TAD 10 further includes memory 202 which includes preprogrammed application programs in program memory 16. The TAD 10 also includes a DTMF generator 212 and a DTMF decoder 204. The DTMF generator 212 and/or the DTMF decoder 204 may be software routines operated by the processor, or may be separate hardware elements within the TAD 10.
The DTMF generator 212 generates analog tones through a codec associated with the processor 18 or voice recorder/playback module 20. The DTMF decoder 204 is typically used, e.g., in remote operation of the TAD 10 to decode which of keys 301-316 are pressed at a remote telephone device. Thus, for instance, the TAD 10 may prompt a remote user calling in to the TAD 10 over a telephone line to "press 1" if they want to listen to their messages, or "press *" if they want to record a message, or "press #" if they want to change their personal greeting. The DTMF decoder 204 will decode the two (dual) frequencies (i.e., DTMF tones) of a response by the user to determine which of keys 301-316 have been pressed. Silence periods are conventionally used between DTMF tones to distinguish between separate keypresses. Thus, if the two frequencies 941 Hz and 1477 Hz are detected, the keypress is interpreted as the user selecting the pound sign "#" key, and the processor 18 would, e.g., proceed to operate the routines necessary to change the outgoing greeting message of the TAD 10.
The programs for the processors and voice prompts in digital telephone devices are typically stored in digital memory at the time that the digital telephone device is manufactured, i.e., while at the factory. The digital telephone devices are tested and shipped to consumers, with pre-installed programs and voice prompts already stored in memory. The memory is typically physically inaccessible to the user without disassembly of the digital telephone device.
Environmental conditions or other factors may cause the contents of the memory to become corrupted. For instance, it is possible for an electrical surge such as may be caused by a lightning strike to disrupt the contents of the memory without destroying the operation of the memory. Moreover, newer features may become available after the digital telephone devices are first shipped, and thus the pre-stored program may become outdated, obsoleting the digital telephone device.
Thus, after installation of the digital telephone device, it may become desirable to re-program, re-store or upgrade portions of the contents of memory, e.g., programs and/or voice prompts. However, conventional digital telephone devices do not allow a user direct access to the memory therein. Nor do such conventional digital telephone devices allow a user to reprogram the memory in the field. Rather, at best, the digital telephone devices must be shipped back to the factory where the memory is either reprogrammed or replaced, or the entire digital telephone device is discarded.
There is thus a need for digital telephone devices having the capability to allow a user to reprogram, re-store or replace the contents of memory after the digital telephone device is installed in the field, without the need to ship the digital telephone device back to the factory.